160 ELEMENTS OF BOTANY. 



196. Cross-Fertilisation and Self- Fertilization. — It was long 

 supposed by botanists that the pollen of any perfect flower 

 needed only to be placed on the stigma of the same flower to 

 insure satisfactory fertilization. But in 1857 and 1858 the 

 great English naturalist, Charles Darwin, stated that certain 

 kinds of flowers were entirely dependent for fertilization on 

 the transference of pollen from one plant to another, and he 

 and other botanists soon extended the list of such flowers until 

 it came to include most of the showy, sweet-scented or other- 

 wise conspicuous kinds. It was also shown that probably 

 nearly all attractive flowers, even if they can produce some 

 seed when self-fertilized, do far better when fertilized with * 

 pollen from the flowers of another plant.* This important fact 

 was established by a long series of experiments on the number 

 and vitality of seeds produced by a flower when treated with 

 its own pollen, or self-fertilised, and when treated with pollen 

 from another flower of the same kind, or cross-fertilised.^ 



197. Wind^Fertilized Flowers.^ — It has already been men- 

 tioned (§ 189), that some pollen is dry and powdery, and 

 other kinds are more or less sticky. Pollen of the dusty sort 

 is light, and therefore adapted to be blown about by the wind. 

 Any one who has been much in cornfields after the corn has 

 " tasseled " has noticed the pale yellow dusty pollen which 

 flies about when a cornstalk is jostled, and which collects in 

 considerable quantities on the blades of the leaves. Corn is 

 monoecious, but fertilization is best accomplished by pollen 

 blown from the " tassel " (stamens) of one plant being carried 

 to the " silk " (pistils) of another plant. This is well shown 

 by the fact, familiar to every observing farmer's boy, that 

 solitary cornstalks, such as often grow very luxuriantly in 

 an unused barnyard or similar locality, bear very imperfect 



1 See Darwin's Cross and Self-Fertilization in the Vegetable Kingdom, (especially 

 Chapters I and II). 



2 On dispersion of pollen see Kerner and Oliver, vol. II, 129-287. 

 8 See Miss Newell's Botany Reader, Part II, Chapter VII. 



